An Organic Light Emitting Diode (OLED) display is a focus in the research field of flat panel displays. The OLED display has lower power consumption, a lower production cost, is self-illuminating, has a wider angle of view, has a higher response speed, and has several other advantages as compared with a Liquid Crystal Display (LCD). At present, the OLED display has taken the place of the traditional LCD in the field of flat panel displays including a mobile phone, a Personal Digital Assistant (PDA), a digital camera, etc., where the design of a pixel circuit is a core technology of the OLED display, and of great significance to the research thereof.